Effects of particle size and content of RDX on burning stability of RDXbased propellants

Particle size and content of RDX are the two main factors that affect the burning stability of RDX-based propellants. However, these effects and the corresponding mechanisms are still controversial. In this work, we investigated the physicochemical processes during burning and the corresponding mechanisms through the technologies of structure compactness analysis on the base of voidage measurement and theoretical interfacial area estimation, apparent burning rate measurement using closed vessel(CV)and extinguished burning surface characterization relying on interrupted closed vessel(ICV) and scanning electron microscope(SEM). The results indicate that the voidage increased with the increase of RDX content and particle size due to the increasing interfacial area and increasing interface gap size,respectively. The apparent burning rate increased with the increase of RDX particle size because of the decreasing RDX specific surface area on the burning surface, which could decrease the heat absorbing rates of the melting and evaporation processes of RDX in the condensed phase. Similarly, the apparent burning rate decreased with the increase of RDX content at pressures lower than around 55 MPa due to the increasing RDX specific surface area. Whereas, an opposite trend could be observed at pressures higher than around 55 MPa, which was attributed to the increasing heat feedback from the gas phase as the result of the increasing propellant energy. For propellants containing very coarse RDX particles, such as 97.8 and 199.4 μm average size, the apparent burning rate increased stably with a flat extinguished surface at pressures lower than around 30 MPa, while increased sharply above around 30 MPa with the extinguished surface becoming more and more rugged as the pressure increased. In addition, the turning degree of u-p curve increased with the increase of coarse RDX content and particle size, and could be reduced by improving the structure compactness.

Blue-detuned optical atom trapping in a compact plasmonic structure

We theoretically propose blue-detuned optical trapping for neutral atoms via strong near-field interfacing in a plasmonic nanohole array. The optical field at resonance forms a nanoscale-trap potential with an FWHM of 200 nm and about ～370 nm away from the nanohole; thus, a stable 3 D atom trapping independent of the surface potential is demonstrated. The effective trap depth is more than 1 m K when the optical power of trapping light is only about 0.5 m W, while the atom scattering rate is merely about 3.31 s^(-1), and the trap lifetime is about 800 s.This compact plasmonic structure provides high uniformity of trap depths and a two-layer array of atom nanotraps, which should have important applications in the manipulation of cold atoms and collective resonance fluorescence.

A new compact structure for a high intensity low-energy heavy-ion accelerator

A new compact accelerating structure named Hybrid RFQ is proposed to accelerate a high-intensity low-energy heavy ion beam in HISCL （High Intensive heavy ion SuperConducting Linear accelerator）, which is an injector of HIAF （Heavy Ion Advanced Research Facility）. It is combined by an alternative series of acceleration gaps and RFQ sections. The proposed structure has a high accelerating ability compared with a conventional RFQ and is more compact than traditional DTLs. A Hybrid RFQ is designed to accelerate 238U34＋ from 0.38 MeV/u to 1.33 MeV/u. The operation frequency is described to be 81.25 MHz at CW （continuous wave） mode. The design beam current is 1.0 mA. The results of beam dynamics and RF simulation of the Hybrid RFQ show that the structure has a good performance at the energy range for ion acceleration. The emittance growth is less than 5% in both directions and the RF power is less than 150 kW. In this paper, the results of beam dynamics and RF simulation of the Hybrid RFQ are presented.

Grain boundaries contribute to highly efficient lithium-ion transport in advanced LiNi_(0.8)Co_(0.15)Al_(0.05)O_(2)secondary sphere with compact structure

LiNi_(0.8)Co_(0.15)Al_(0.05)O_(2)(NCA)secondary particles with high tap density have a great potential for high volumetric energy density lithium(Li)-ion power bat-tery.However,the ionic conductivity mechanism of NCA with compact structure is still a suspense,especially the function of grain boundaries.Herein,we sys-tematically investigate the Li-ion transport behavior in both the primitive NCA(PNCA)secondary sphere densely grown by single-crystal primary grains and ball-milled NCA(MNCA)nanosized particle to reveal the role of grain bound-aries for Li-ion transport.The PNCA and MNCA have comparable Li-ion dif-fusion coefficients and rate performance.Moreover,the graphene nanosheet conductive additive only mildly affects the Li-ion diffusion in PNCA cathode,while which severely blocks the Li-ion transport in MNCA cathode.Through high-resolution transmission electron microscopy and electron energy loss spec-troscopy,we clearly observe Li-ion depletion at lower state of charge(SOC)and Li-ion aggregation at high SOC along the grain boundaries of PNCA secondary particles during high-rate lithiation process.The grain boundaries can construct an interconnected Li-ion transport network for highly efficient Li-ion transport,which contributes to excellent high-rate performance of compact PNCA sec-ondary particles.These findings present new strategy and deep insight in design-ing compact materials with excellent high-rate performance.